1.Field of the Invention
The present invention relates to a resin composition containing a uniformly dispersed olefin polymer used for electrophotographic toner and also relates to the toner derived from the resin composition. The toner containing the resin composition has a good offset preventing property.
2.Description of the Prior Art
Photoconductive materials are generally applied for electrophotographic methods, to developed electrostatically latent images on a surface of photosensitized body by various means. The latent images are successively developed by electrostatically adhering the toner. The tonered images are transferred onto a copy sheet such as paper etc. and fixed by heat, pressure, solvent vapor or the like to get the duplicate. Various methods and devices have been developed for the fixation step of aforesaid toner images on the copy sheet. Today the most popular method, however, is a thermal press method using hot roller. So the fixing method using hot roller is carried out under heat and pressure that leads to a rapid and effective fixing with excellent thermal efficiency.
But, according to this method, the hot roller surface is brought into contact with toner and melt it, and the melted toner is transferred and print to the copy sheet. Subsequently, there is a problem that the adhered toner residuum on the hot roller transfers on the next copy sheet, which is called as offset problem.
Some methods have been proposed in order to prevent this problem. For example,
(1) To increase the melt viscosity of the toner.
(2) To improve the roll release property of the toner, wherein disperse uniformly olefin polymer such as low molecular waxy polypropylene.
Further, method (1) has another weak point of insufficient toner melt and poor toner fixation caused by heat supply shortage accompanying with operation speed up. Notwithstanding an excellent effect being expected by addition of the low molecular weight wax in the method (2), but yet sufficient wax dispersion has not been achieved.
For example, in the wax kneading process to prepare toner (Japanese Patent Publication No. 2304/1977), the variation of particle size distribution in the vinyl polymer and the olefin polymer which are fed to the kneading machine causes errors in the feeding amount due to the maldistribution of the powder, and the differences of dispersed state in the course of time. Besides the low molecular weight polypropylene wax generally has no compatibility with almost all of vinyl polymers such as styrene copolymer resin, normally has a melting point of 100.degree. C. and above, and is difficult to disperse uniformly. Thus the wax has a tendency of disadvantage to require a large quantity for use in toner. Wax rich parts which formed in toner particles by the addition of a large amount of the wax have influence on the electrostatic charge of the toner, and also have a disadvantage that sharp images cannot be obtained. In order to improve the dispersion by the kneading time extension, the resin in the toner is exposed to a high temperature for a longer period and is worsen to cause bad effect contrary.
Besides, in the method of adding the wax in the polymerization of the vinyl monomer, the wax participates the polymerization and has influence on the molecular weight of the resulting resin. The monomer also grafts on the wax and has effect on the glass transition temperature (Tg) of the vinyl polymer. Furthermore, the wax has a disadvantage of reducing the action of roll release agent due to the decomposition of the wax itself.
Therefore, it has been required to establish the technology for uniformly dispersing the wax into the vinyl polymer so that a particle diameter of 0.5-3 .mu.m can be obtained on the wax. Such diameter is sufficient for preventing the offset problem without disadvantageous effect on the toner properties.